High-power pulse generator



Jan. 25, 1949. J. E. GORHAM ETAL 2,459,809

HIGH POWER PULSE GENERATOR Filed Jan. 14, 1943 2 Sheets-Sheet l as ea 90 I 3 1 4 92w 92 84 34 I +-4 86 INVENTOR 38 JOHN EGORHAM V lNG SAGER 6 -%w.

A TTORNE Y Jan. 25, 1949. J. E. GORHAM ETAL 2,459,809

HIGH POWER PULSE GENERATOR Filed Jan. 14, 1943 2 Sheets-Sheet 2 Ij II/IIIIIII i i INVENTOR JOHN E. GORHAM I50 I46 76 BY IRVI c SAGER F c. .8 214 4 ATTORNEY Patented Jan. 25, 1949 2,459,809 HIGH-POWER PULSE GENERATOR John E. Gorham, Spring Lake, and Irving Sager, Deal, N. J.

Application January 14, 1943, Serial No. 472,352

6 Claims.

(Granted under the act of amended April 30, 1928;

The invention described herein may be manufactured and used by or for the Government for governmental purposes, Without the payment to us of any royalty thereon.

This invention relates to radio transmitters, particularly for pulse-echo work, and relates more especially to modulating means for such transmitters.

Systems for modulating a transmitter by means of a spark gap are already known, and the primary object of the present invention is to generally improve such systems.

Some prior spark gap modulating systems require auxiliary control electrodes or other means to start the spark. Some require an air-blast or other means to quench or stop the spark. Some employ rotating electrodes with appropriate driving gear. One of the main objects of our invention is to dispense with the need for any of the aforesaid auxiliary means, with their attendant disadvantages.

In terms of practical apparatus, power for the spark gap modulator may be obtained from a lowvoltage A.-C. source by using a step-up transformer and a rectifier. Such a source usually needs filter elements, and these are bulky and ex pensive when large power is to be handled. Another more specific object of our invention is to devise a modulator adapted to operate from such a power source having poor filtration or low capacitance. In fact, one efiicient form of our apparatus may be said to operate better with low capacitance and poor filtration than with good filtration.

Another object of our invention is to provide a spark gap modulator which will generate pulses of extremely high voltage and amperage while using equipment which is compact, simple, inexpensive, and dependable. Other objects of our invention are to provide a spark gap modulator which is characterized by long life, which is devoid of moving parts, and which requires the use of only two low-power rectifier tubes, thereby conserving on tubes. Another object is to provide a spark gap modulator which is insensitive to wide changes of temperature, thus making it suitable for use in either polar or equatorial regions.

Still further objects are to provide a spark gap modulator capable of generating pulses which may be varied in Width narrow or a very wide pulse as desired, and which may be varied in frequency over a very wide range of say two or three to one by simple turning a knob. The ability to readily change the keying rate helps avoid intentional interference by someto provide either a very March 3, 1883, as 370 0. G. 757) one who may have gained knowledge of the k8 ing rate previously used. Along this line, still another object is to provide a pulse generator or modulator which is relatively non-periodic. This is no advantage with modern pulse-echo systems in which the receiver oscilloscope may be triggered by the transmitter pulse yet it is of advantage in making it more difiicult to interfere with the transmitter pulses.

To accomplish the foregoing and other objects which will hereinafter appear, our invention resides in the spark gap modulator elements and their relation to one another and to the transmitter, as hereinafter are more particularly de-- scribed in the specification and sought to be defined in the claims. The specification is accompanied by drawings in which Figure 1 is a side elevation of a spark gap modulator embodying features of our invention;

Figure 2 is a schematic wiring diagram of a transmitter including the spark gap modulator shown in Figure 1;

Figure 3 illustrates a detail of a section of the cathode and is taken approximately in the plane of the line 3-3 of Figure 1;

Figure 4 illustrates a detail of the anode and is taken approximately in the plane of the line 44 of Figure 1;

Figure 5 is a plan view of the spark gap mechamsm;

Figure 6 is a section taken approximately in the plane of the line 6--6 of Figure 5;

Figure '7 is a vertical elevation taken approximately in the plane of the line 1-1 of Figure 5;

Figure 8 is a, bottom view of the spark gap modulator shown in Figure 1; and

Figure 9 is a plan view of a detailed portion of Figure 5, drawn to enlarged scale in order to clarify the construction.

Referring to the drawing and more particularly to Figure 2, the transmitter comprises a 11-0. source generally designated S, and an ultrahigh-frequency transmitter generally designated T. The transmitter is keyed by high-power pulses generated in a spark gap modulator generally designated K. This consists of a network of series-connected inductors and shunt-con nected condensers with spark gaps connected diagonally therebetween as shown. The arrangement is such that the condensers are charged in parallel, but are discharged in series, so that the resulting pulse has the cumulative potential of all of the condensers. The network K is connected to the D.-C. source S through an impedance Z, said impedance functioning to isolate the source S from the network K when the gaps break down. In this way a single pulse is obtained. Another network W may be inserted between the network K and the transmitter T in order to better shape or square the pulse.

The pulsewoltage which maybegenerated in this fashion. is so" high that itimay be used directly as a polarizing potential for the transmitter tube, that is, a positive pulse may be ap plied directly to the anode of the tube. In the specific circuit which we have illustrated; the

tube is operated in invertediashionpthe:anode.

being grounded, and a negative pulse being ap-: plied to the cathode of the,tube. With. either arrangement the tube will oscillate'only intermittently, and only while polarized by thepulse potential.

The impedance Z is importantiin ordento. pre= vent a continuous arc orspark which might draw hundreds of amperes. This impedance is made suificientlyhigh so that the condensers cannot recharge fast enoughto support-the arc, and the 1 spark istherefore immediately extinguished; Whenonce-extinguished the spark-will not strike again-until the condensers build up thenecessary high voltage.

Although we have referredto the source S as a D.-C'.' source; the modulator is more directly operable from an ordinary 60-cycle Ai-C. line, the'sourceS then consistingsimply of a voltagevarying-'- means, a step up transformer; and a rectifier. In the present case, the voltage-varyingmeans-isanautotransformer Hi. The trans- 7 former consists ofa=primary i2; and a secondary Hethe output-ofwhich is supplied'to diodes l6 and" i8? These-are raced in opposite directions;

and in proper direction'to obtain either aposithre or negative pulse; as desired. Condensers 2s and 22" are' connected" in V series between the impedance Z and ground as shown, so that the circuit constitutes an elemental form of volt-- age doubler. No special elaborate filter is provided to smooth the D.-C. output and, in fact, a source oflow capacitance is preferablewhen' us ing an inductive impedance- 8B, as showni The inductiveimpedance is preferable because it is more .eficient' in avoiding the heat dissipation which accompanies the use of a resistiveimpedance. With aresistive-impedance, however, the

D.-C. source may be a source having a smooth gap, to the second condenseriand' thence through the-second gap; totlie third condenser; etc-1, with out-flowing= through the chokesatall; This re sultsinaedischarge thi'ough all of 'the condensers' and-gaps in series; so that theipulse-potential is equal to: the sum of'the individual condenser potentials; In a typical casethebreakdown volt age' forieachsection of "the network, that is, for each condenser and gap; may be say 5,000 volts, in whichrcase the output pulse when using-say eight gaps, as here illustrated, will be about 40,080

volts.

In respectito theoperation of the circuit, itmay' be :explained: thatxthe inductance of. the chokes in network K is negligible compared to the far greater inductance of the impedance Z. During charging of the condensers the circuit may be considered as comprising only the source S, the

impedance Z, and the storage condensers M connected in parallel atithe. output of the impedance ZL During discharge of the condensers it, the circuit may be considered as consisting only of the network K in series with the waveshaper W, for the impedance Z in effect separates the network i; from source S. The time requiredto charge thecondensers to maximum potential value before breakdown of the spark gaps must be larger than the lowest period at which the system is likely to be operated.

Whenusing an inductive impedance, the impedance Z itself acts as a voltage doubler. The flow of current from source S will tend to produce oscillations, for the initial potential. rise is carried on by the ine tia of the inductor Z to a value nearlytwice as igh as'that of the source. In'the absence of the spark gaps thiswouldbe followed by a voltage drop which overswings, then another voltage rise which overswings, and soon; resulting inad'amped train of oscillations which would finally settle do vn to a steady state voltageequal to the-voltage of the source 5. However, thespark gaps are adjusted to break down at a voltage somewhat below the peakvoltage of the first'upward swing. The resulting spark is -a short cir-- cuit which pulls the voltage down to zero and thus abruptly arrests-theincipient train of oscillations, whereupon the condensers begin to be charged from zero, and the charge again rises to nearly double voltage because ofthe action of the inductor 'Z.

The wave-shaper W may take any of a considerable number of forms. A typical wave-shaper is'one'oi the Guilleman type lines; The network shown here is far simpler but is adequate for the present purpose. It comprises an inductor 30inseries witha parallel resonant circuit'made up of a capacitor 32and an inductor 34.

TheGuilleman type line would be similar to the network W but would have three more parallel resonant circuits following that shown. The simplified network W here shown is employed merely to reduce the amount of apparatus required, for we have found that by empirically setting the value or" the capacitor 32 and-the inductor 3 5- the succeeding three parallel resonant circuits may be eliminated. The resulting pulse wave does not have as good a square shape as'would be obtained when using the complete Guilleman' type line, but is good enough for the present purpose.

The particular transmitter here shown is intended to operate at a frequency of about 600 me. and employes a so-called Vt-158 tube, which is described in detail in copending applications of Harold A. Zahl, Serial No. 473,556, filed January: 251 1943, entitled, Electronic tube;'and1I-Iarold. A. Zahl, Glenn F. Rouse; and John E." Gorham,

Serial No. 495,65 filed July 29, .1943; nOWPatent No. 2,454,298'issued November '23, 1948; en, titled Electronic tube. The said tube. consists of two sets of triode electrodes, arranged in pushpull, with grid-to-grid and anode-to-anode loops all disposed within a vacuum tube envelope; In" Figure 2 the anodes 38 and 38 areconnected byan anode loop it, and the grids 32 and Mi are connected by a grid loop Grid bias maybe applied at 38. The heating circuits for'the cathodes. have been omitted. The cathodes are tuned by means of an ext'ernalloop 55), adjusted by ashorting bar 52. The anodes are also tuned by an external loop 54, adjusted by a shorting bar 56. Power is taken from the loop 54 over any desired form of transmission line, but in the present case, for purposes of simplification, power is assumed radiated directly from a dipole antenna 58.

To modulate the transmitter, the cathodes may be grounded at 60 and a positive pulse from the modulator may be applied to the anode at 62. However, in the specific case here illustrated, the anodes are grounded at E2 and a negative pulse from network K and wave-shaper W is applied to the cathodes at 60. The rectifiers I 6 and !8 are properly poled to provide the necessary negative pulse.

It will be understood that although a particular transmitter and oscillator tube have been mentioned, our modulator system may be used with other transmitters and tubes.

Other features of the invention will be understood by reference to the structural arrangement of the parts of the network K. Referring to Figure 1, a chassis plate 64 is secured to a front panel '66. A row of spark gaps 68 (Figures 1 and 5) is disposed above the chassis plate 64. Each spark gap comprises a cathode 'I'Oand an anode 12. The electrodes are relatively movable to adjust the gap therebetween, this preferably being conveniently and accurately done by means of a control handle I-I (Figure 1) at the front of the panel. The gap adjustment may be used to control the output voltage, for the breakdown voltage depends on the length of the gap. Also, for any given gap length the control handle H may be used to compensate for dissipation or wear of the electrodes. This wear is very slight and unnoticeable, being only a matter of say 0.001 inch per day, so that a set of electrodes will last for years. In practice the operator will ordinarily tune the transmitter once a day or once every few days, and while doing so will vary the control knob H for proper adjustment of the modulating voltage, and this will make up for any preceding wear of the electrodes.

A row of condensers 14 (Figures 1 and 8) is mounted beneath the chassis plate 64, and rows of chokes I6 and I3 are mounted at each side of the condensers 74. By properly locating the chokes and condensers along the bottom of the chassis beneath the spark gaps at the top of the chassis, these parts may be connected by short direct vertical leads (not shown). At the same time, the spark gaps are disposed at the top for easy observation and adjustment. A row of series-connected chokes 80 may also be disposed along the bottom of chassis 64, all of these chokes making up the single impedance Z previously referred to.

Considering the spark gap structure in greater detail, the cathodes I0 and the anodes I2 rest on V-grooved brass blocks 84 and 86, as is best shown in Figures 3 and 4. The electrodes are rods of a suitable high-temperature metal, for example tungsten or molybdenum, and are held in position by appropriate fiat springs 83 and 90, the outer ends of said springs being secured to the outer ends of the blocks by screws 92 (Figures 1, 5, and 7) Blocks 84 are secured in spaced parallel relation on an insulation strip 94, and blocks 86 are secured to another insulation strip 96. The insulation for strips 94 and 96, and also the chassis plate 64, may be a material known commercially as Mycalex. Strip 94 is mounted on two preferably insulation posts 98 (Figure 1), the upper ends being held by screws I00 (see Figure 5) and the lower ends being similarly secured to a base plate I02. In the present case, plate I02 is stationarily mounted on the chassis plate by means of four stand-off insulators I04, two of which are Visible in Figure l.

The insulation strip 96 is similarly mounted at the upper end of two stand-oh insulators I06 (Figures 1 and 7), as by means of screws I08 (Figure 5). The lower ends of posts I06 are carried by a cross bar I I 0 (Figures 1, 6, and '7) which is either formed integrally with or is rigidly secured to a slide II2 (Figure 6). Slide H2 is dovetail-shaped in section, and is guided between bottom plate I 22 and guide plates I I6, which may be adjustably secured on plate 12, to guide the slide II 2 with a close fit.

Referring now to Figures 1, 5, and 9, the knob or handle H is secured at the outer end of a rotatable shaft IIB. This passes through a stationary bearing block I53 mounted at the forward end of base plate I552. Collars I28 are secured to shaft I I 6 at opposite sides of bearing Ii 8, thereby holding the shaft against axial movement. The inner end of shaft IE5 is threaded, preferably with a very fine, accurately-tooled thread. This is received in a mating female thread, formed in the slide H2 previously referred to. It will be evident that by rotating the shaft M6, the slide H2 will be moved either forward or backward, thereby varying the spacing between the stationary and movable electrodes of the entire row of spark gaps.

In order to eliminate slack or lost motion, which might interfere with accurate control at the handle H, we employ compression springs I 25, which are disposed between the stationary bearing H8 and the forward end of the movable slide H2. These compression springs take up play or slack in the shaft bearing and in the thread while the shaft is being turned in either direction. As a further precaution, and in order to introduce a desired amount of fn'ction against rotation of the shaft, a plate 525 is secured in front of the slide II 2, said plate being slotted at I28 (Figure 7) and provided with a clamp screw I30. Plate I26 is threaded to mate with the threaded shaft H5, and by tightening the clamp screw I 30 the slotted thread may be tightened around the shaft to introduce any desired degree of friction.

The compression springs I24 are preferably carried by rods I32 (Figure 9) which are secured at one end and are slidable at the other. In the present case, the forward ends I 34 are slidable through the bearing H8. The inner ends 536 are threadedly received in slide H2. Intcgrally formed collars H33 are provided, which act as bolt-heads bearing against the plate I26 and securing the same to the forward end of slide II2. Thus, the rods I 32 act not only as supports and guides for the compression springs, but also as bolts to hold the friction plate I 28 on the forward end of slide II2.

As is known, the cathode of a spark gap is volatilized or sputtered far more rapidly than the anode, the wear of the anode being negligible compared to that of the cathode. In th present structure, the cathodes are of relatively small diameter. We prefer a smal1-diameter rod to a large-diameter rod because We have found that with a large-diameter rod a crater is formed at the center which makes it diiiicult to readjust the electrodes to make up for wear. If. on the other hand, a small-diameter rod is employed, it is eaten away entirely across its. end surface, thus zneasoo presenting a generally flat working end to the anode. As thecathodes are worn away, the wear may be made-up by readjustment at the handle H; After a substantial amount of wear, say a fifth-inch, corresponding to say a nalf-years use, thehan'dle H may be rotated in the opposite rection to back the anodes far away from the cathodes, whereupon the cathode rods may be slidicutiby hand until they touch or nearly touch theanodes. By advancing the anodes, the oathodes will automatically be aligned, and by then backing away the anodes, a uniform gap space willz'b'e provided at all of the spark gaps. This same .nrechanism facilitates replacement of the cathodes, but the wear is very gradual, and a single set of electrodes operating continuously dayiand; night .willllast for years.

The anodes l2 may be made of larger diameter, and it is ordinarily unnecessary to advance or to replace the same, hence they may be made relatively short. The anode preferably bear against positive stops in order to fix the same in position, whereas the cathodes are held solely by the pressure of the springs '38. InFigure the springs of the right hand spark gap have been broken away, and it will be seen that the V- grooved block 86 is provided with a stop screw at Add abutting the endof'anode 72.

The storage condensers are cylindrical in form andare bolted at their upper ends to the chassis plate 0.4. Figure. 1 shows one of the condensers 14 held by a screw I' l-2', while Figure 8 shows the entire line of condensers. It will be understood that connection to the terminals of the condensers is :made at the upper and lower ends, the lower connection being indicated by an appropriate soldering lug its (Figure 1).

'The chokes l5 and 7B are supportedv on horizontal rods of insulation I (Figures 1 and 8) which, in turn, are mounted on vertical insulati'orr posts M3 (Figure 1). Each of the chokes 16 shown in Figure 2 is structurally wound as two pancake-shaped coils, preferably with a honeycomb winding. These two coils are connected in series. Each pair of coils is received on one of the horizontal rods Hi5. These rods maybe cut away to overlap at their ends, the overlapping ends being screwed to the posts M8. The screws for thispurpose are indicated at I in Figure 8.

In the particular case here illustrated, the imped'anco Z is an inductive impedance and is made up or four iron-cored inductors disposed side by side, indicated at 80 in Figure 8. If desired, these-may be suspended from upright insulators [-52 (Figure l), which, in turn, are secured to the chassis plate e l.

While the invention is applicable to a variety of conditions as to pulse frequency and power, etc., an illustrative example of some of the quantitative dimensions which we employed in one particular spark gap modulator are given hereina'fter. For a pulse frequency of say 250 cycles and a potential of about 20,000 volts'and pulse width of about '1 microsecond, we used chokes it and T3 having an inductance of about 75 millihenri'es. The storage condensers l4 had a capacitance of 0.01 microfarad. The impedance Z totalled 48 henries. The network was supplied with power from an ordinary 110-vo1t, cycle source, which was :fed through a Variac autotransformer (0 to 110 volts) to a step-up transformer, the secondary of which delivered a voltage of about 1500 volts. This was doubled by the voltage-doubling action or the rectifier to a peak voltage of. about 3.000 volts. in turn, was

8 againdoubled-by the impedance Ztoa peakrvalue of about 6000 volts. The storage condenserstend to'charge up to that voltage, but the-gaps were set to break down at say 5000- volts. With 8 gaps the voltage was 0,000, of which about half was lost in the wave-shaper.

The rectifier tubes 5-0 and i8 were ordinary tubes of the type 866A, and the series capacitors 20 and 22 each had a Value-of 1.0 microfarad.

The spark gaps employed cathodes made of tungsten rodshaving a diameter of 3% of ani-nch, and a length of say 1 /2 inches, though even a length of A, inch is adequate for long. life. The anodes were made of tungsten rods having a diameter of about inch.

The wave-shaping circuit shown in Figure 2 used an inductor 30 having a value of about microhenries, a capacitor 32- having a value ofabout 0.0006 microfarad, and an inductor 3d having'a value of about illmicrohenries.

It will be understood that the foregoing quantitative dimensions have been given solely bywayof illustration and not in limitation of the invention. The dimensions 'will vary widely with changes in pulse power, pulse voltage, pulse frequency, etc. Moreover, if a resistive impedance is used instead. of an inductive impedance, the smoothing condensers 20- and- 22 may be much larger in magnitude. The use of a resistive impedance reduces the efficiency somewhat because of heat dissipation in the resistor, but, even so, the system is a highlyefiicient one comparedto other keying systems. When using the more em?- cient inductive impedance, it is-desirable not to use unnecessarily largecondensers at 20 and 22, because if made too large, thespark will tend to persist.

it is believed that the construction and operation of our improved sparkgap keyer will be understood from the foregoing detailed description.

The storage condensers are charged until the potential thereon equalsthe critical value for breakdown of the spark gaps, whereupon the gaps conduct. Although the condensors are charged in parallel because the chokes I6 and 18 do not appreciably impede the relatively slow charging current, the condensors are discharged in series because the chokes efiectively block the sudden pulse delivered when the gaps break down. The sparks are quenched when the potential on the condensors falls to a value below that needed to maintain the spark, and this takes place very quickly, in fact, almost instantly, because the high impedance Z prevents rapid recharging of the condensers. Because the pulse potential is the cumulative potential of all of the condensers, the pulse obtained is a very powerful one, yet it is so rapidly quenched that a pulse of only a few microseconds duration may be obtained if desired.

The frequency of the pulse depends on the values of the impedance Z, the storage condensers, the D.-C. input voltage from the source S, and the gap spacing, An increase in gap spacing results in an increase in potential up to thelimit of the available charging potential. The duration of the pulse is a function of the load, and of the size of the storage condensers, as well. as the shaping circuit W. The pulse frequency varies with the input voltage for a constant gap spacing. The pulse voltage varies with the gap spacing, but a change in gap spacing will incidentally vary the pulse frequency somewhat. If one wishes to change the pulse frequency while maintaining the pulse voltage, theinput voltage shouldbe changed by moving the controlknob oi the Variac autotransformer I'll. If one wishes to change the pulse voltage while maintaining the pulse frequency, it is necessary to change the gap spacing, and to then somewhat change the input voltage in order to compensate for any change in pulse frequency which may arise as an incident to the change in gap spacing. The ease with which the pulse frequency may be changed is of considerable benefit in the field, in order to overcome attempted enemy interference with the transmission.

Many of the advantages of the present transmitter and keyer will be recognized from the foregoing description, but by way of summary, it may be pointed out that the keyer is compact, simple, light, devoid of moving parts, and employs only two low-power rectifier tubes, yet is capable of delivering extraordinary high power output. The structure conserves on tubes. It is rugged, and is insensitive to wide temperature variation, so that it may be satisfactorily used in arctic or desert regions. The keyer does not require an air blast to quench the spark, nor an auxiliary electrode or auxiliary pulse circuit to start the spark. The keyer may be designed to produce a narrow or a wide pulse, as required, and the pulse frequency may be varied over a wide range of say, 2 or 3 to 1, by simply turning a knob to change the input voltage. Because the pulse is not strictly periodic, it is more diii'icult for a hostile transmitter to interfere with the present transmitter. There is also the advantage that pulses from other nearby friendly pulse-echo systems will not interfere with effective reception from the present system, because the neighboring systems will have either a periodic pulse, or a nonperiodic pulse randomly different from the present non-periodic pulse.

It will be apparent that' while we have shown and described our invention in a preferred form, many changes may be made in the structure disclosed, without departing from the spirit of the invention as sought to be defined in the following claims.

We claim:

1. Apparatus for modulating a transmitter, said apparatus comprising a potential source, an inductive impedance, a network having a plurality of condensers, chokes connecting said condensers in parallel, and spark gaps connecting said condensers in series, means for applying said potential source in series with said impedance to said network, whereby said condensers charge in parallel until the voltage thereon equals the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potential of said condensers, said impedance in combination with said parallel condensers forming an oscillatory circuit and serving to increase the charging voltage on said condensers, said impedance also functioning to impede the charging current to quickly quench the spark, and mean to feed said pulse to the transmitter to modulate same.

2. Apparatus for modulating a transmitter tube, said apparatus comprising a D.-C. potential source, means to vary the output potential of said source, an inductive impedance, a network having a plurality of condensers, chokes connecting said condensers in parallel, and spark gaps connecting said condensers in series, means for applying said potential source in series with said impedance to said network whereby said condensers charge in parallel until the voltage thereon equals the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potential of said condensers, said impedance in combination with said parallel condensers forming an oscillatory circuit and serving to increase the charging voltage on said condensers, said impedance also functioning to impede the charging current to quickly quench the spark, and means to feed said pulse to an electrode of the transmitter tube in order to drive the tube.

3. Apparatus for modulating a transmitter tube, said apparatus comprising a D.-C. potential source, an inductive impedance, a network having a plurality of condensers, chokes connecting said condensers in parallel, and spark gaps connecting said condensers in series, means for applying said potential source in series with said impedance to said network whereby said condensers charge in parallel until the voltage thereon equal the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potential of said condensers, said impedance in combination with said parallel condensers forming an oscillatory circuit and serving to increase the charging voltage on said condensers, said impedance also functioning to impede the charging current to quickly quench the spark, a wave-shaping network in the discharge path of said condensers to square the wave-form of the resulting pulse, and means to feed said pulse to an electrode of the transmitter tube in order to drive the tube.

t. A transmitter for pulse-echo work, said transmitter comprising a D.-C. potential source having minimum size smoothing capacitors, a large inductive impedance, a network having a plurality of condensers, chokes connecting said condensers in parallel, and spark gaps connecting said condensers in series, means for applying said potential source in series with said impedance to said network whereby said condensers charge in parallel until the voltage thereon equals the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potential of said condensers, said impedance in combination with said parallel condensers forming an oscillatory circuit and serving to increase the charging voltage on said condensers, said impedance also functioning to impede the charging current to quickly quench the spark, a wave-shaping network in the discharge path of said condensers to square the wave-form of the resulting pulse, and a transmitter tube having a tank circuit associated therewith, the output from the wave-shaping network being applied to the transmitter tube to act as the D.-C. driving potential for the same.

5. Apparatus for modulating a transmitter, said apparatus comprising a D.-C. potential source including a low voltage A.-C. supply, a step-up transformer for said supply, a rectifier and filter capacitors, said capacitors being of minimum size for poor filtration, an inductive impedance, a network having a plurality of condensers, chokes connecting said condensers in parallel, and spark gaps connecting said condensers in series, means for applying said potential source in series with said impedance to said network, whereby said condensers charge in parallel until the voltage thereon equals the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potential of said condensers, said impedance in combination with said parallel condensers forming an oscillatory circuit and serving aesaeoo to increase the charging'voltage on said condensers, said impedance also. functioning to impede the charging current to quickly quench the spark, a wave-shaping network in the discharge path of said condensers to square the wave-form of the resulting pulse, and means to feed said pulse to the transmitter tube in order to modulate same.

6. Apparatus .for modulating a transmitter tube, said apparatuscomprising a D.-C. potential source, means to vary the output potential of said source, an inductive impedance, anetwork having a plurality of condensers, chokes connecting. saidcondensersin parallel, and spark gaps; connecting said condensers in series, said spark; gaps being disposed in spaced collateral relationship, .thezcathodes .ofsaid spark gaps being relativeiylong, small-diameter rods of high-temperature metal, the anodes of said spark gaps beingv relatively short; large-diameter rods of high-temperature emetal, said .cathodesbeing carried by a first. insulation strip and projecting transversely from one edge of said strip, said anodes being carriedby asecond insulation strip and-projectingtransversely'from. one edge of said second strip, saidstrips being mounted for adjustment toward or away from .one another in order tov change. the gapzspacing between the cathodes and;.anodes,the cathode rods being. slidably held by. friction springs. inorder-xtobe axially movable tomake .up for wear of the, said rods, means for applying saidpotential source in series with said impedance to. said. network whereby said condenserscharge .in'parallel until the voltage thereon equals the breakdown voltage of said spark gaps, whereupon said condensers discharge in series so that the resulting pulse has the cumulative potentia-Lof: said condensers'and means to 12 feed said pulseto the; transmitter to modulate same.

JOHN E, GORHAM. IRVING SAGER.

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